The invention relates generally to group decoders for multiple antenna multiuser communication channels.
Multiple access techniques such as code division multiple access (CDMA) allow multiple users to efficiently share limited communication resources. The performance of such multiple access techniques can potentially be further improved by using multiuser detection, in which user signals are jointly detected rather than considered as interfering noise to each other. Unfortunately, optimal multiuser decoding techniques have high decoding complexity which are often infeasible for practical systems. It has been proposed to divide users into groups, where each group is jointly detected based on a decision statistic obtained via zero-forcing operation with or without decision feedback. See M. K. Varanasi, “Group Detection for Synchronous Gaussian Code-Division Multiple-Access Channels,” IEEE Transactions on Information Theory, Vol. 41, No. 4 (July 1995). Group detection can potentially relieve the tension between good performance and low detection complexity. More recently, it has been proposed, in the context of sequential group detectors used in an uncoded Gaussian CDMA channel with BPSK modulation, to maximize the asymptotic symmetric energy over all partitions satisfying a maximum group size constraint. See J. Luo et al., “Optimal Grouping Algorithm for a Group Detection Feedback Detector in Synchronous CDMA Communications,” IEEE Transactions on Communications, Vol. 51, pp. 341-46 (March 2003). Unfortunately, this metric is not applicable to a fading multiple access channel with random channel fluctuations where users possibly employ outer codes of different rates and different modulation schemes.
The problem of determining the optimal grouping strategy, accordingly, still represents a challenge, in particular as attention shifts to wireless fading multiple access channels where the receiver employ multiple antennas.